The Microstructure Of Directionally Solidified Ternary Al-Cu-Si Eutectic Alloy

The binary aluminum alloy with directional solidification was concentrated at present,but a few of ternary or multicomponent aluminum alloys with directional solidificationwere researched. Al-13.6Cu-6Si alloy inserted into the vacuum melting furnace. Afterallowing time for melt homogenization molten alloy was poured into graphite crucibles(200mm in length24mm ID and20mm OD) specimen of Φ20×200mm were solidifiedunder steady state conditions In order to study the effect of the pulling rates on themicrostructure of the directionally solidified alloy, the Al-13.6Cu-6Si alloy was carriedout under the a temperature gradient of5K/mm and pulling rates of1,5,10,20,25and35mm/min respectively. The microstructure of the cross-section and vertical section ofdirectional solidification samples was observed. by using the optical microscope (OM)and the scanning electron microscope (SEM), and the mechanism of its eutectic growthwas analyzed. The effect of growth rates on performance with directional solidification inAl-13.6Cu-6Si aluminium alloy is investigated by the means of hardness tests and so on.And Using originPro7.5software fitting determination microhardness and solidificationparameter relations.The experimental results show that, the growth direction of the directionalsolidification alloy is opposite to that of heat flow. The middle part of the microstructurefor directional solidified rod was homogeneous, directional characteristic was moreobvious. The microstructure of the alloy was consisted of α-Al, θ-Al₂Cu, β-Si phases byX-ray diffraction and optical microscope.When the pulling rates were as low as1mm/min,the microstructure of directly solidified Al-13.6Cu-6Si alloy is consisted of (α-Al+θ-Al₂Cu) two-phase eutectic and (α-Al+β-Si+θ-Al₂Cu) three-phase eutectic. When thepulling rates increased up to5mm/min,the primary θ-Al₂Cu phase could be observed inthe alloy.(α-Al+β-Si+θ-Al₂Cu)ternary eutectic cells distribute among (α-Al+θ-Al₂Cu)binary eutectic cells and make binary eutectic cells separated to be relatively independent"islands".Under the same temperature gradient, the array of the directionally solidifiedmicrostructure is more symmetrical and well-regulated with the decrease of drawing rate, the structure was changed from the cellular to the dendrite, and the microstructure isincreasingly refined, the hardness of Al-13.6Cu-6Si aluminum alloy is from88HV to200HV.